The role metal ions play in influencing biochemical reactions is certainly multifaceted. With sulfur-containing enzymatic species, metal ion coordination often is found. Yet little is known about metal ion influences in these systems. In this proposed study sulfur atom lability in the presence of certain metal ions, notably Zn(II), Cd(II), Co(II), and Fe(III), is to be investigated. In particular we are interested in materials that contain "inorganic" sulfide, mercaptide metal bonds and polysulfides. Mercaptide and bridged mercaptide complexes will be synthesized and studied as models for ferredoxins and metallothioneins. Our interest will be directed particularly toward synthesis, oxidation-reduction properties, metal-sulfur bond rupture and stereochemical features of these complexes. The mechanism of sulfur atom transfer and transport by these metal complexes will be an important objective of this research . Nuclear magnetic resonance studies of the kinetics of ligand rearrangements and metal-sulfur bond rupture form a substantial part of this investigation, particularly with the metal ions zinc(II) and cadmium (II). Appropriate materials will be synthesized, characterized and studied by well-established coordination chemistry techniques.